1. Field of the Invention
The present invention relates to a scratch testing apparatus for performing a scratching test while gradually increasing or decreasing a load. and more particularly, to a scratch testing apparatus, in which load applied using a tip gradually increases or decreases as a tester head, to which the tip is attached, moves horizontally, so that scratching operation may be performed as changing a load applied to a test specimen.
2. Description of the Related Art
A tape testing method, a bending test, a press-fitting testing method and a scratching testing method are included as examples of testing methods generally used for testing adhesiveness between an object material and a thin film of coating or paint performed to maintain and reinforce characteristics of the object material. A tape testing method is to determine whether coating or paint comes off or not when a tape (an adhesive tape) is attached on and then detached from a surface of an object material. The bending test is the method of measuring a bending load at which a coating or paint comes off. A press-fitting testing method is to determine adhesiveness of a coating or paint through inspecting a crack and an indentation existed on a coated or painted surface after an object material is press-fitted. Finally, a scratching testing is a method of determining the critical load based on scratches formed by scratching a coated or painted surface.
Here, the scratching testing method is convenient and provides quantized measurement. Therefore, the scratching testing method is the most widely used in industries.
During a scratching test, adhesiveness between materials is determined based on color shifting of a coating, paint, or a thin film or a change of plasticity which appears on the surfaces of the materials.
A method of applying a predetermined load on a surface and scratching the surface is used to determine the adhesiveness. However, a number of tests should be performed and a lot of test specimens are needed in order to determine a critical load.
Therefore, scratching testing method, in which a load applied to a test specimen changes as a tip moves from a beginning point to a ending point of the scratching, is standardized and disclosed in ASTM D7027, ISO 1518, and ISO 12137-2.
According to the method above, a load at the time of generating a deformation by a scratch on a surface is detected, and thus adhesiveness between the surface and the material and a property of the material are determined by measuring the load.
According to the ASTM D7027 standards, the critical load shall be determined by gradually increasing a load from 2N to 50N with respect to a displacement of 100 mm at a rate of 100 mm/s and observing whitening phenomenon of the material.
Furthermore, according to ISO 1518 and ISO 12137-2 standards, a scratching test shall be performed by forming a scratch at a rate of 200 mm/s to determine the critical load of scratching paint or a coated plastic.
However, since the scratching method shall be performed at a relatively fast rate, it is difficult to control the load and displacement of a testing apparatus, and it is difficult to synchronize the beginning of movements, transportations, and the stopping of movements along the vertical axis and the horizontal axis.